plane of incidence

In physics, the plane of incidence is a plane that contains both an incident line, such as a ray of light, and the normal (a line perpendicular) to a surface at the point where the ray strikes. This concept is crucial when understanding how waves or particles interact with surfaces.12

When light or another wave hits a surface, it can be reflected or refracted. The laws governing these phenomena state that the incident ray, the reflected ray, and the normal all lie within this same plane of incidence. The angle of incidence, which is the angle between the incident ray and the normal, is equal to the angle of reflection. This principle is fundamental to understanding optics, including how mirrors work and how light bends when passing from one medium to another, as described by the law of refraction or Snell's law.21